The problems of coal dust are well known. This problem is encountered throughout the coal handling industry—at the mine, at transfer points, and at utilities or at other points of utilization. The problem may be compounded as a result of the close proximity of transfer points and utilities to populated or environmentally sensitive areas.
Conventional dust suppression systems include both mechanical and chemical methods. For instance, dust collection equipment includes devices which capture entrained dust, induce the dust to settle, or contain the dust. The most common dust suppression method, however, is the wetting of coal with water. Water is inexpensive and large quantities can be added to eliminate dust. But the addition of water decreases the specific heating value of the coal.
In addition to water alone, other aqueous additives are known and used. These include solutions containing surfactants. Aqueous foams are known. Still further, aqueous compositions comprising asphalt emulsions or other organic coating materials may be used.
It is also known to apply oils and resins to reduce or eliminate dust. Oil spraying includes the use of crude, residual, waste or fuel oils.
Other liquids that may be applied to the coal to reduce dust include both synthetic and natural polymers. For instance, plant-material-containing liquids including sugar and sugar-related products are known. Other polymers that collect or stick to the dust particles have also been used.
Unrelated to the issue of reducing coal dust, it is also desirable to improve the complete combustion of coal. Carbon in fly ash results from the incomplete combustion of coal. Therefore, it is desirable to reduce the carbon in ash in order to reduce the overall amount of fly ash emission from a coal combustion chamber. Also, low carbon fly ash is easier to dispose of and more easily captured than high carbon fly ash by electrostatic precipitators that are often used to control particulate emissions.